Electronic structure of graphene on single crystal copper substrates

TL;DR

This study examines how graphene interacts electronically with copper single crystals, revealing substrate-dependent effects on the Dirac point, band gap, and surface state protection after air exposure.

Contribution

It provides detailed insights into the electronic structure of graphene on Cu(111) and Cu(100), including effects of air exposure and oxygen intercalation, using advanced spectroscopic techniques.

Findings

Graphene on Cu(111) shows a -0.3 eV Dirac shift and 250 meV gap.

Oxygen intercalation on Cu(100) increases Dirac offset to -0.6 eV and enlarges the gap.

Graphene protects the Cu surface state from air exposure.

Abstract

The electronic structure of graphene on Cu(111) and Cu(100) single crystals is investigated using low energy electron microscopy, low energy electron diffraction and angle resolved photoemission spectroscopy. On both substrates the graphene is rotationally disordered and interactions between the graphene and substrate lead to a shift in the Dirac crossing of $\sim$ -0.3 eV and the opening of a $\sim$ 250 meV gap. Exposure of the samples to air resulted in intercalation of oxygen under the graphene on Cu(100), which formed a ($\sqrt{2} \times 2\sqrt{2}$)R45$^{\rm o}$ superstructure. The effect of this intercalation on the graphene $\pi$ bands is to increase the offset of the Dirac crossing ($\sim$ -0.6 eV) and enlarge the gap ($\sim$ 350 meV). No such effect is observed for the graphene on Cu(111) sample, with the surface state at $\Gamma$ not showing the gap associated with a surface superstructure. The graphene film is found to protect the surface state from air exposure, with no change in the effective mass observed.